How is power portrayed in Act 3 of Shakespeare's play Macbeth?

We see how Macbeth's power has grown since he's become king.  Now that he's secured his position by murdering Duncan, he can hire someone to kill Banquo and Fleance for him.  So, he hires murderers to commit the crime for him by convincing them that Banquo is to blame for the hardships they've endured in Scotland (as, apparently, Scotland has not prospered under Macbeth's reign).  His ability to get others to do his dirty work...

We see how Macbeth's power has grown since he's become king.  Now that he's secured his position by murdering Duncan, he can hire someone to kill Banquo and Fleance for him.  So, he hires murderers to commit the crime for him by convincing them that Banquo is to blame for the hardships they've endured in Scotland (as, apparently, Scotland has not prospered under Macbeth's reign).  His ability to get others to do his dirty work indicates how much his power has gained. 

Moreover, Macbeth's power in his relationship with Lady Macbeth has dramatically increased.  She does not rule him anymore.  Now, he has ordered the murders of Banquo and Fleance without consulting her or even involving her in his plans at all.  In fact, he even lies to her, giving her instructions about how to treat Banquo at their dinner that night, a dinner that he knows Banquo will not be alive to attend.  He tells her, "Be innocent of the knowledge, dearest chuck, / Till thou applaud the deed" (3.2.52-53).  Lady Macbeth used to make all their plans, and now Macbeth makes his plans alone.

In the banquet scene, we can see the way Macbeth's power over his subjects has grown.  He can act completely insane, and his subjects allow him to go on and on, insisting that they are only concerned for his health.  He speaks to an empty seat, reacts to behavior only he can see, and threatens and shouts, and when he demands that they remain, they do so because they are scared to disobey him.  He can command just about anything, and he will be obeyed.  The scene between Lennox and the other lord lets us know that Macbeth's treachery is suspected, and he's known as a tyrant, one who holds essentially supreme power.